Firstly it is important to have investigated all symptoms with your veterinarian to make sure that they are not the result of bacterial infection or reactions to parasites or insects, or other illnesses or viruses that create similar reactions, for example a respiratory virus. All those have a limited life and have medications available to assist.
An allergic reaction is a difficult problem for the horse owner, can be quite frustrating and also debilitating for the horse.
Normal healthy horses have antibodies that can challenge the allergens and irritants that are around them all the time. However at some point the immune system becomes hyposensitised to these allergens and a reaction is set off whereby an overabundance of antibodies are produced, these then release a flood of prostaglandins, histamines etc . The symptoms we see are the reactions to this rush of antibodies and the subsequent response. Once this process has been triggered the horse tends to react even more easily with each exposure and symptoms become more intense. There is no known reason for this, it is not an aspect of breed, age, gender etc.
The common signs are either skin reactions - lumps, heat, itching; or more often the respiratory system is affected, with runny noses (clear) inflamed nasal passages, cough, runny eyes, head movements (mainly from the irritated nose) puffing , generally under par in themselves.
There are many triggers and it would seem that it can either be a particular new antigen or the collective effect of too many types that then get over the top of the horses natural protection. Examples are dust, hay spores, moulds, some foods or supplements, insect bites, even sunlight, sometimes treatments for other problems can create a trigger.
Skin Allergies - Most often seen as lumps, sometimes hot and itchy. These often pass once the cause has gone, for example an eruption of a certain insect that bites that while they cause a direct skin reaction, the saliva can also create an allergic reaction. Skin reactions can be from a food trigger too. Often these itchy lumps can be eased with an application of cool gel, maybe a herbal anti- inflammatory, an anti-itch cream - It is better to try more natural responses initially than drugs as these may create side effects and stress the immune system.
Other skin triggers can simply be products that in most horses are fine but in your horse he reacts – usually easy to identify and solved by not using that product.eg a certain detergent used In washing a saddle blanket , or even a particular fabric in a rug or saddle blanket.
Skin tests are available to try and identify the allergen or allergens, often a combination. Once identified prevention is the best option.
Respiratory allergies – Sometimes called heaves or RAO recurrent airway obstruction – similar to asthma in people. Common to this is a clear runny nose, sometimes just a light clear trickle.
When tested this discharge has no bacteria – unlike infectious discharges linked to respiratory illnesses. Coughing and wheezing may or may not be present, often the eyes are runny and in extreme cases the horse may start head shaking. Respiratory allergies are debilitating to the horse and will affect performance and often attitude to training.
Finding the Cause - In both cases (skin and respiratory) finding the cause is helpful so that with a change in the management of the horse, it may be eliminated. As well as skin tests some good observance, note keeping and detective work are very important. The owner knows the horse best, with skin allergies check for insects and bites, eliminate all products applied to the skin, saddle blankets, wraps etc and introduce them back one by one. The cause may surprise you, it could be quite innocuous in other horses but not for this one.
Feed testing is just the same, start from scratch and gradually reintroduce each foodstuff and supplement watching for signs to worsen. Feedstuff allergies can stem from breathing in spores from the feed or within the gut itself as two thirds of the immune system is contained in the walls of the intestines.
The solution is to remove the culprit or culprits. Firstly direct good management of never having horses in a dusty or mouldy environment, scrupulous cleaning of feed bins and managers. Not using strong chemicals. Damp all feed and wash hay, damp bedding. Keep the horse out in a fresh air environment. Even though spores may not be the actual trigger , all moulds ,dust and spores are irritants and so can exacerbate the response to an allergen, or prevent or slow down recovery.
Sadly some trees will affect the horse when pollens are let go and then it’s either remove the horse from the area while this happens or clothe him and use a nasal cream as a block to inhaling the pollen.
Corticosteroids and other drug therapies are available from your veterinarian, they can ease the symptoms to give the horse some relief but are not a cure, nor are they a long term solution. They can create new problems for the horse, for example laminitis can be a result of long term use.
The other option is to help the immune system and some good results have been seen with a boost of vitamins C, A and D plus a product called Rutin – a flavonoid. While not purported to be a cure –it can provide a natural aid to the horse to increase his own ability to challenge the antigens.
Finally there is also some evidence that feeding an Omega 3 product such as flax oil or rice bran does assist to reduce the inflammatory reaction. There is a limit to the amount of liquid oil that can be fed daily but stabilised rice bran will provide a good source of Omega 3 in a palatable and moist form.
Allergic reactions are a complex issue and the problem may often be a combination of triggers and reactions, so the solution is a multiple of various factors ; from good management, good observance and knowledge of the horse, removing obvious potential triggers and providing assistance to reduce symptoms, improving the immune response to help the horse challenge the antigens.